Brazil Launches Fourth Riachuelo-Class Submarine and Commissioning of Third Submarine

Brazil has taken another major step in modernising its undersea fleet, combining the launch of its fourth Scorpène-derived submarine with the commissioning of the third Submarine in the series during a high-profile ceremony at the Itaguaí Naval Base in Rio de Janeiro state.

On 26 November 2025, the Brazilian Navy christened S43 Almirante Karam (formerly named Angostura), the fourth diesel-electric submarine of the Riachuelo class, and formally brought S42 Tonelero into operational service. It was the first time the navy presented two submarines in a single event, underlining how far the country’s Submarine Development Programme (PROSUB) has progressed since it was launched with France in 2008.

From French Scorpène to Brazilian Riachuelo Class

The Riachuelo class (S-BR) is Brazil’s customised version of the French Scorpène-class diesel-electric attack submarine, developed by Naval Group and built locally by Itaguaí Construções Navais (ICN). Compared with the baseline Scorpène, the Brazilian boats feature a stretched hull of about 70–72 metres and increased displacement to improve range, endurance and payload.

According to the Brazilian Navy and Naval News reporting, Almirante Karam is part of the first generation of Riachuelo-class submarines to be fully produced in Brazil, reflecting the maturity of ICN’s industrial base after years of technology transfer in welding, structures, piping and electrical systems. More than 250 Brazilian technicians have been trained in France and now oversee the complete production chain at Itaguaí, from steel cutting to integration and testing.

The Riachuelo class is intended to patrol Brazil’s vast “Amazônia Azul” (Blue Amazon) – the country’s huge exclusive economic zone – protect offshore oil and gas fields and provide a modern deterrent in the South Atlantic.

The PROSUB Deal: Cost, Scope and Quantity

The current submarine force renewal is the core of PROSUB (Programa de Desenvolvimento de Submarinos), a long-term strategic partnership between Brazil and France.

Under a 2008 defence pact, Brazil ordered four enlarged Scorpène-type conventional submarines and agreed a second package covering the design support for its first nuclear-powered attack submarine, SN-10 Álvaro Alberto, as well as the construction of a new shipyard and submarine base at Itaguaí. Contemporary Brazilian and French sources put the overall programme value at roughly US$10 billion (about €6.7 billion at the time).

Within this package, the quantity of conventional boats is fixed at four Riachuelo-class diesel-electric submarines:

• S40 Riachuelo

• S41 Humaitá

• S42 Tonelero

• S43 Almirante Karam

In parallel, PROSUB funds the design and non-nuclear systems for the Álvaro Alberto nuclear-powered submarine and the extensive industrial and support infrastructure at the Itaguaí Naval Complex, including a shipyard, piers, dry docks and maintenance facilities.

Riachuelo-Class Timeline: From S40 to S43

The four conventional submarines have followed a staged but steadily advancing build schedule:

S40 Riachuelo
Riachuelo, the lead boat, had its hull laid down in 2010, was launched on 14 December 2018, began sea trials in 2019 and was commissioned on 1 September 2022, becoming Brazil’s first operational Scorpène-derived submarine.

S41 Humaitá
The second boat, Humaitá, was launched in December 2020 and undertook an extensive trials programme – including deep dives and torpedo firings – before being commissioned on 12 January 2024 at the Ilha da Madeira Submarine Base.

S42 Tonelero
The third submarine, Tonelero, was launched on 27 March 2024 at Itaguaí, in a ceremony attended by Brazilian President Luiz Inácio Lula da Silva and French President Emmanuel Macron. After starting sea trials in 2024, Tonelero was formally commissioned during the 26 November 2025 ceremony, entering front-line service as Brazil’s third Riachuelo-class boat.

S43 Almirante Karam
The latest boat, S43 Almirante Karam, was christened and launched on 26 November 2025 at the same Itaguaí event. Originally known as Angostura, the submarine received its new name in honour of a Brazilian naval hero. Almirante Karam will now undergo fitting-out and trials before joining the fleet later in the decade.

With these milestones, Brazil now has three Riachuelo-class submarines in service and one newly launched, consolidating a modern conventional submarine force in the South Atlantic.

Almirante Karam and the Riachuelo-Class: Key Specifications

• Type: Attack submarine (SSK)
• Displacement: Approximately 1,900 tons surfaced (up to 2,200 tons submerged)
• Length: 70.62 meters (231 ft 8 in)
• Beam: 6.2 meters (20 ft 4 in)
• Propulsion: Diesel-electric system including four MTU diesels and a Jeumont-Schneider electric motor
• Speed: Up to 21 knots (39 km/h; 24 mph) submerged
• Test Depth: 400 meters (1,300 ft)
• Endurance: Over 45 to 70 days at sea
• Complement: 32–35 crew members
• Armament:
  • 6 x 533 mm (21 in) torpedo tubes
  • 18 x F21 heavy-weight torpedoes
  • 8 x SM39 Exocet anti-ship missiles
  • Up to 30 naval mines
• Sensors & Systems: Equipped with the Naval Group SUBTICS combat management system and various Thales sonar and electronic warfare systems 

Stepping Stone to Brazil’s Nuclear Submarine

The ceremony at Itaguaí also highlighted that PROSUB is not limited to conventional submarines. The same industrial and human capital underpinning the Riachuelo-class is being used to support Brazil’s ambitious nuclear submarine project, centred on the SN-10 Álvaro Alberto.

In 2025, the Brazilian Navy signed two new contracts worth more than €526 million with Naval Group for the nuclear-powered submarine programme – one for specialised engineering and construction work linked to the LABGENE nuclear power generation laboratory, and another for consultancy on additional systems for the conventionally armed nuclear submarine. Current planning foresees delivery of Álvaro Alberto from around 2034 onwards.

By successfully launching Almirante Karam and commissioning Tonelero, Brazil has shown that its Scorpène-based Riachuelo class is no longer just a symbolic transfer of technology but a mature industrial capability. The fourth submarine’s arrival in the water, alongside a growing nuclear effort, signals that the Brazilian Navy’s submarine arm is entering a new era – with local industry at its core and long-range undersea operations firmly in view.